STR:

1. In the Python console, execute:
   import re;wx.CallLater(2500, re.search, 'a+b', 'a'*20000000)
2. Press escape to close the console before that runs.

Result:
NVDA freezes, as expected. However, I can't do anything with the keyboard to restart NVDA.

From discussion on IRC, I tried commenting out nvdaControllerInternal_typedCharacterNotify in nvdaHelper/remote/typedCharacter.cpp and was able to use the keyboard to restart if NVDA froze this way.

It looks like when that part of NVDAHelper calls back into Python, NVDAHelper freezes.